[Bug 1841634] Re: CP link triggers lost when record is async

[Andrew Johnson via Core-talk <core-talk@aps.anl.gov>]

“a lot of churn”? — please explain.

I believe the rpro mechanism does exactly what we need here (but I admit
I was looking at the 3.15 version of the code, not 7.0). The scanOnce
code is pretty simple and short so duplicating it won’t be hard, the
only difference being that the queue processor checks pact and sets rpro
(and putf perhaps?) if needs be. The word Force isn’t quite right for
the API name though, I’ll keep thinking on that.

Why are you thinking we might have to introduce dbNotify here? Now
/that/ would be churn.

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https://bugs.launchpad.net/bugs/1841634

Title:
  CP link triggers lost when record is async

Status in EPICS Base:
  Confirmed
Status in EPICS Base 7.0 series:
  Confirmed

Bug description:
  From Benjamin Franksen:

  Here is a small self-contained database to reproduce this:

  record(calcout,"input") {
      field(CALC,"A<4?A+1:A")
      field(INPA,"input")
      field(ODLY,"1")
      field(OUT,"input.A CA")
  }
  record(calcout,"output") {
      field(ODLY,"1.5")
      field(INPA,"input CPP")
      field(CALC,"A")
      field(TPRO,1)
  }
  record(calc,"check") {
      field(INPA,"input CPP")
      field(INPB,"output CPP")
      field(CALC,"A==B")
  }

  Processing "input" (caput input.PROC 1) starts the test. The "check"
  record should eventually settle to 1 (but doesn't).

  With 7.0.3 I get this output:

  scanOnce: dbProcess of 'output' # initial CPP processing
  scanOnce: dbProcess of 'output'
  scanOnce: dbProcess of Active 'output' with RPRO=0
  scanOnce: dbProcess of 'output'
  scanOnce: dbProcess of Active 'output' with RPRO=0

  Note how this says "with RPRO=0".

  And camonitor says:

  franksen@tiber: ~ > camonitor input output check
  input                          <undefined> 0 UDF INVALID
  output                         2019-08-27 16:02:16.106413 0
  check                          2019-08-27 16:02:16.106617 1
  input                          2019-08-27 16:02:26.498483 1
  check                          2019-08-27 16:02:26.498721 0
  input                          2019-08-27 16:02:27.493734 2
  output                         2019-08-27 16:02:27.993908 1
  input                          2019-08-27 16:02:28.489068 3
  input                          2019-08-27 16:02:29.484350 4
  output                         2019-08-27 16:02:29.984458 3

  I think the difference in behavior between processing due to a CPP
  input link versus processing due to a PP or CA output link is quite
  surprising.

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